Dielectric antennas are devices that radiate or receive radio waves at a chosen frequency of transmission and reception, as used in for example in mobile telecommunications. In general, a dielectric antenna consists of a volume of a dielectric material disposed on or close to a grounded substrate, with energy being transferred to and from the dielectric material by way of monopole probes inserted into the dielectric material or by way of monopole aperture feeds provided in the grounded substrate (an aperture feed is a discontinuity, generally rectangular in shape, although oval, oblong, trapezoidal ‘H’ shape, ‘<->’ shape, or butterfly/bow tie shapes and combinations of these shapes may also be appropriate, provided in the grounded substrate where this is covered by the dielectric material. The aperture feed may be excited by a strip feed in the form of a inicrostrip transmission line, grounded or ungrounded coplanar transmission line, triplate, slotline or the like which is located on a side of the grounded substrate remote from the dielectric material). Direct connection to and excitation by a microstrip transmission line is also possible. Alternatively, dipole probes may be inserted into the dielectric material, in which case a grounded substrate may not be required. By providing multiple feeds and exciting these sequentially or in various combinations, a continuously or incrementally steerable beam or beams may be formed, as discussed for example in the present applicant's U.S. patent application Ser. No. 09/431,548 now U.S. Pat. No. 6,452,565 and the publication by KINGSLEY, S. P. and O'KEEFE, S. G., “Beam steering and monopulse processing of probe-fed dielectric resonator antennas”, lEE Proceedings—Radar Sonar and Navigation, 146, 3, 121–125, 1999, the full contents of which are hereby incorporated into the present application by reference.
The resonant characteristics of a dielectric antenna depend, inter alia, upon the shape and size of the volume of dielectric material, the shape, size and position of the feeds thereto and also on the shape, size and position of the groundplane. It is to be appreciated that in a dielectric antenna, it is the dielectric material that radiates when excited by the feed. This is to be contrasted with a dielectrically loaded antenna (DLA), in which a traditional conductive radiating element is encased in a dielectric material that modifies the resonance characteristics of the radiating element. As a further distinction, a DLA has either no, or only a small, displacement current flowing in the dielectric whereas a dielectric resonator antenna (DRA) or high dielectric antenna (HDA) has a non-trivial displacement current.
Dielectric antennas may take various forms, a common form having a cylindrical shape or half- or quarter-split cylindrical shape. The dielectric medium can be made from several candidate materials including ceramic dielectrics.
Dielectric resonator antennas (DRAs) were first studied systematically in 1983 [LONG, S. A., McALLISTER, M. W., and SHEN, L. C.: “The Resonant Cylindrical Dielectric Cavity Antenna”, IEEE Transactions on Antennas and Propagation, AP-31, 1983, pp 406–412]. Since then, interest has grown in their radiation patterns because of their high radiation efficiency, good match to most commonly used transmission lines and small physical size [MONGIA, RK and BHARTIA, P.: “Dielectric Resonator Antennas—A Review and General Design Relations for Resonant Frequency and Bandwidth”, International Journal of Microwave and Millimetre-Wave Computer-Aided Engineering, 1994, 4, (3), pp 230–247]. A summary of some more recent developments can be found in PETOSA, A., ITTIPIBOON, A., ANTAR, Y. M. M., ROSCOE, D., and CUHACI, M.: “Recent advances in Dielectric-Resonator Antenna Technology”, EEE Antennas and Propagation Magazine, 1998, 40, (3), pp 35–48.
A variety of basic shapes have been found to act as good dielectric resonator structures when mounted on or close to a ground plane (grounded substrate) and excited by an appropriate method. Perhaps the best known of these geometries are:    Rectangle [McALLISTER, M. W., LONG, S. A. and CONWAY G. L.: “Rectangular Dielectric Resonator Antenna”, Electronics Letters, 1983, 19, (6), pp 218–219].    Triangle [ITTIPIBOON, A., MONGIA, R. K, ANTAR, Y. M. M., BHARTIA, P. and CUHACI, M.: “Aperture Fed Rectangular and Triangular Dielectric Resonators for use as Magnetic Dipole Antenmas”, Electronics Letters, 1993, 29, (23), pp 2001–2002].    Hemisphere [LEUNG, K. W.: “Simple results for conformal-strip excited hemispherical dielectric resonator antenna”, Electronics Letters, 2000, 36, (11)].    Cylinder [LONG, S. A., McALLISTER, M. W., and SHEN, L. C.: “The Resonant Cylindrical Dielectric Cavity Antenna”, IEEE Transactions on Antennas and Propagation, AP-31, 1983, pp 406–412].    Half-split cylinder (half a cylinder mounted vertically on a ground plane) [MONGIA, R. K., ITTIPBOON, A., ANTAR, Y. M. M., BHARTIA, P. and CUHACI, M: “A Half-Split Cylindrical Dielectric Resonator Antenna Using Slot-Coupling”, IEEE Microwave and guided Wave Letters, 1993, Vol. 3, No. 2, pp 38–39].
Some of these antenna designs have also been divided into sectors. For example, a cylindrical DRA can be halved [TAM, M. T. K. and MURCH, R. D.: “Half volume dielectric resonator antenna designs”, Electronics Letters, 1997, 33, (23), pp 1914–1916]. However, dividing an antenna in half, or sectoring it further, does not change the basic geometry from cylindrical, rectangular, etc.
High dielectric antennas (HDAs) are similar to DRAs, but instead of having a full ground plane located under the dielectric resonator, HDAs have a smaller ground plane or no ground plane at all. DRAs generally have a deep, well-defined resonant frequency, whereas HDAs tend to have a less well-defined response, but operate over a wider range of frequencies. HDAs can take the same variety of preferred shapes as DRAs. However, any arbitrary dielectric shape can be made to radiate and this can be useful when trying to design the antenna to be conformal to its casing.
In both DRAs and HDAs, the primary radiator is the dielectric resonator. In DLAs the primary radiator is a conductive component (e.g. a copper wire or the like) and the dielectric modifies the medium in which the antenna operates, and generally makes the antenna smaller.